1. Field of the Invention
The present invention relates to a shutter blade device, and more particularly to a blade device of a vertically running focal plane shutter.
2. Related Background Art
There will be explained a conventional shutter blade device, with reference to the attached drawings.
FIGS. 4 to 6 and 8 illustrate a conventional shutter blade device.
Referring to FIG. 4, a shutter base plate 1 is provided with an aperture 1a, and shafts 1b, 1c. An auxiliary arm 2 is rotatably mounted on the shaft 1b. A driving arm 3 is provided with a hole 3a and is rotatably mounted on the shaft 1c. A slit blade 4 is rotatably mounted, on the auxiliary arm 2 by a pin 4a, and on the driving arm 3 by a pin 4b. Similarly, cover blades 5, 6, 7 are rotatably mounted, on the auxiliary arm 2 respectively by pins 5a, 6a, 7a, and on the driving arm 3 respectively by pins 5b, 6b, 7b.
In the conventional shutter blade device, when the slit blade 4 and the cover blades 5, 6, 7 are retracted from the aperture la and mutually superposed as shown in FIG. 4, the pins 4a, 5a, 6a are superposed respectively with the cover blades 5, 6, 7, while the pins 5b, 6b are not superposed with the adjacent cover blades 6, 7.
On the other hand, when the slit blade 4 and the cover blades 5, 6, 7 are extended as shown in FIG. 6, the pins 4a, 5a, 6a are not superposed with the adjacent cover blades 5, 6, 7 while the pins 5b, 6b are superposed with the adjacent cover blades 6, 7. In this manner the pins 5a, 6a, 7a, 5b, 6b repeatedly assume a state superposed with the adjacent cover blades and a non-superposed state, with the movement of the shutter blades.
In the course of running motion of the shutter blades, there exits a state shown in FIG. 5, where the pin 4a is released from overlapping with or starts to overlap with the cover blade 5. A similar position exists also for each of other pins 5a, 6a, 5b, 6b.
FIG. 8 is a cross-sectional view along a line A--A in FIG. 5. As shown in FIG. 8, there is required a step t1 for each of said pins 4a, 5a, 6a, 5b, 6b. Without such step t1, a projection t2 formed by caulking collides with the cover blade 5, thereby damaging said blade (see FIG. 9). When the step t1 shown in FIG. 8 is intended to be formed for avoiding such drawback, the slit blade 4 has to be provided with a bent portion 4e. Said bent portion 4e shows a lowered strength than in the peripheral area, because of stress concentration in the caulked or bent portion, crack formation in the bent portion or hardening by working, thereby becoming inadequate for a high-speed shutter.